The invention relates to an apparatus for testing the adhesive strength of a coating on a substrate, comprising a device for generating mechanical stress in a predefinable surface region of the coating, and an evaluation unit which comprises a device for image acquisition and a device for assessing the cracks which arise. The invention further relates to a method for testing the adhesive strength of a coating on a substrate, in which method, in a first method step, mechanical stress is applied to at least one predefinable surface region of the coating, and, in a second method step, the surface region is investigated for damage by means of an evaluation unit.
Coatings can be applied to substrates by a multiplicity of methods which are known per se. The coating can increase the mechanical or thermal load-bearing capacity of the substrate or can serve for decorative purposes. To ensure reliable operation, a sufficient adhesive strength of the coating on the substrate is required. Thus, methods of the type mentioned in the introduction are used for testing and assessing the adhesive strength in the development of novel coatings or for quality assurance during the manufacture of coated components.
A method of the type mentioned in the introduction is known from DE 100 43 155 A1. According to this known method, a partial region of the coating is loaded by means of a test specimen. Then, the crack pattern which arises around the impression of the test specimen and the area content of released regions are investigated by means of an optical microscopy image.
However, this known method has the disadvantage that the coated substrate has to be transported between the loading with the test specimen and the optical microscope. This makes an additional working step necessary, which reduces the efficiency of the method. Furthermore, substrates may be mixed up and/or there may be a mix up between a plurality of test impressions applied to a substrate. This reduces the reliability of the method.
If the coated substrate is to be used at elevated operating temperatures, the adhesive strength of the coating may be higher or even lower on account of different coefficients of thermal expansion between the base material and the coating at relatively high temperatures. Therefore, it is necessary to test and assess the adhesive strength at the planned operating temperature. This requires that the loading by the test specimen and the evaluation by optical microscopy are effected at a uniform temperature in order to avoid thermal stresses during the measurement. As a result, the known method requires the substrate which is at an elevated temperature to be transported, which is technically complex and dangerous for the operating personnel.
The invention is therefore based on the object of developing a measurement method of the type mentioned in the introduction in such a way that the measurement can be made in a more reliable and simple manner. A further aim is to make it possible to carry out the measurement at an elevated temperature.